The invention is a process and a device for reading out binary information magnetically stored on a transparent magnetic layer. Transparent magnetic layers have recently become well known in photographic films, where they are used to record information for illumination and/or processing of photographic films according to the invention and to maintain data for access in devices used in processing. Because of the requirement that photographic films can not be altered essentially in their capacity to store images and thus in their transparency, these magnetic layers can contain only very little material. The magnetic fields of recorded signals are correspondingly weak; they may be lower by a factor of 200 than fields for customary sound and data recordings on nontransparent magnetic tapes or disks designed exclusively for that purpose.
Special measures must thus be taken for capturing and processing magnetic signals which make up the kind of magnetic code as, for example, described in the U.S. Pat. No. 4,987,439. Special amplification and means for evaluation have been developed as, for example, disclosed in the U.S. Pat. No. 4,964,139 for processing weak signals produced by magnetic heads. There a circuit with a single filter 18 is described whose purpose is to eliminate interference signals like the intrinsic noise of a pre-amplifier. It is extraordinarily difficult to tune a filter to multiple interference frequencies caused by various different recording speeds or densities.